With your engine off, when you spin the wheels does your engine turn over as well? If so your clutch is locked up and that would explain your problem.

If not I'm going to guess that your shoes are dragging a bit and that your idle is set a little too low. Try trimming between 1/16" and 1/8" off the end of each clutch shoe. That will lighten them up a bit and cause them to engage at a higher rpm. Either that or you could try to find a stiffer clutch spring to do the same thing.

Once your clutch is free you can finish setting your idle.

Enjoymentboy